Fewer new chemicals chasing resistant weeds?

Producers shouldn't spend too much time waiting for the next miracle herbicide to come along. If recent history is any indication, weed control for the foreseeable future is going to be primarily trait-based, says Darrin Dodds, Extension cotton specialist in Mississippi.

Dodds, speaking at Cotton Incorporated's Crop Management Seminar in Tunica, Miss., pointed out that precious few new herbicide are in the pipeline, and the history of existing herbicides indicate that their golden age is past.

“Glyphosate was discovered to have herbicidal properties in 1970. Metolachlor (Dual), which we depend on for control of Palmer amaranth, was first synthesized in 1972. Dicamba, another product we're starting to use in burndowns, was first awarded a patent 40 years ago. Synthesized during World War II, 2,4-D is over 60 years old. Atrazine, which is still being used on 60 percent to 70 percent of the corn acres, was first synthesized in 1952. The sulfonylurea herbicides were synthesized in 1975; however, some of the bleaching herbicides were introduced as late as 2001. So we're not seeing a lot of new developments in weed control.”

There are also risks associated with developing new herbicides, notes Dodds. “Generally speaking, you're looking at 8 years to 10 years. You're also looking at $250 million to $300 million to develop a new herbicide that may or may not see widespread use.”

Dodds talked about some of the new trait-based technologies coming in line over the next few years, most of which offer resistance to multiple herbicides.

GlyTol, H2 and HPPD-resistance, from Bayer CropScience - The GlyTol gene provides similar levels of glyphosate resistance as Roundup Ready Flex in cotton, but contains a different gene.

Bayer's H2 technology is a combination of the GlyTol trait and the LibertyLink trait that conveys resistance to Bayer's glufosinate (Ignite) herbicide.

GlyTol cotton will likely be available in 2009, but without insect protection. H2 will likely be available in 2010, also without insect protection. For soybeans, GlyTol will be offered with resistance to HPPD-inhibiting (bleacher class) herbicides in 2014. It will be combined with the LibertyLink gene in 2016.

LibertyLink, Bayer CropScience - The trait has been available in cotton for a few years, but in the Mid-South there is very limited acreage, mostly due to variety performance, according to Dodds. However, Bayer has licensed its LibertyLink technology to Monsanto for use in Monsanto's corn and soybean lines, as part of Monsanto's SmartStax package. SmartStax “is an 8-way cassette of insect and herbicide resistance.” (SmartStax is a collaborative agreement between Monsanto and Dow AgroSciences).

LibertyLink soybeans, which are coming on line in 2009. “will require some fundamental changes in mindset compared to the Roundup Ready system,” Dodds said. “If you let weeds get some size on them before spraying Ignite, not only are you not going to kill weeds, you could bust your budget.

“It is a good system, but we have to keep several things in mind, such as spray volume, tip selection, temperature at the time of application, species we're targeting.”

Optimum GAT, DuPont - contains glyphosate and ALS tolerance. “The glyphosate resistance is conferred from a different gene than with Roundup Ready technology and acts in different way. ALS tolerance confers resistant to all five classes of ALS chemistry. The products that DuPont will target with the technology include Classic, Harmony and FirstShot; however, other products may may be added in the future.”

In corn, Optimum GAT will most likely be offered in 2010, said Dodds. “There are plans to include it with Bayer's LibertyLink trait. So essentially, you'll have options for LibertyLink, a glyphosate option with GAT and ALS tolerance. The traits for soybean will most likely be released in 2011.”

Dodds noted that the upside of Optimum GAT is that it will offer another competing gene for glyphosate tolerance in the marketplace. “If you have multiple genes competing in the marketplace in several varieties, that's got to be good for the grower, and hopefully bring that price down.”

On the downside, “It could allow for the increased use of ALS inhibiting herbicides. The ALS chemistry is a good chemistry if it's managed properly.

“Another concern about the Optimum GAT is the availability of hybrids and varieties. It's essentially a DuPont technology, so it stands to reason it's going to be available in Pioneer soybeans and corn. The question is will competing seed companies allow a competing gene to compete with its varieties or hybrids?”

DHT, or Dow AgroSciences Herbicide Trait - offers resistance to 2,4-D and the ‘fop’ family of chemistries, graminicides such as Assure II, Hoelon and Fusilade. It does not confer ‘dim’ resistance, such as to Select Max. “It's going to take some education and thought as far as product selection is concerned.”

In corn, the DHT could be offered in 2012 in conjunction with the SmartStax package. In cotton and soybeans, DHT could be offered in 2013 in conjunction with glyphosate resistance.

One of the pros is the use of additional chemistries for resistance management. “For those who have had issues with 2,4-D drift in the past, this will protect you from some of those issues. However, I have a great concern that anytime we have crops where we apply 2,4-D over the top, we may set ourselves up for more drift problems.

“There is also the problem of crops becoming weeds. If you have a corn hybrid with SmartStax with DHT, you're going to have to figure out what to spray to kill it if it becomes a weed. It's really going to take some education on product selection.”

HPPD resistance - resistance to the bleacher class of herbicides like Callisto, Impact, Laudis, Balance Pro. In soybeans, it will probably be offered in 2016. There is the possibility for potential development in cotton.

Dicamba tolerance, which was discovered by researchers at the University of Nebraska, has been inserted into soybeans, which can be sprayed with up to 5 pounds of active ingredient per acre. Monsanto is developing the technology, but no timetable has been given for its release.